The manufacturing of window frames is a complex process. Broadly described, this process includes two parts. The first part comprises the cutting, machining and welding frame elements to form rectangular window frames. The second part includes the assembly of hinges, seals, locks, thermos panes, bug screens, and packaging for shipping.
The first part of the process, including the assembly of window frames, includes the most difficult operations in the manufacturing of vinyl and aluminum windows. This portion of the process is carried out in the frame machining and welding room. Long extrusions are handled over machinery and in tight spaces. These extrusions are set in jigs and are carefully aligned with the bed of each machine. Precise cutting, machining and welding are critical as dimension tolerances are very small. Verification of work quality requires frequent measurements and an extensive knowledge of all the extrusion profiles at hand. These operations require skills and concentration at all times to avoid errors.
In the past, several systems were developed to facilitate the machining of extrusions that are used in the window manufacturing industry. Some examples of the systems found in the prior art are:    U.S. Pat. No. 5,022,143 issued to J. J. Kautt on Jun. 11, 1991;    U.S. Pat. No. 6,294,044 issued to M. Schwaiger on Sep. 25, 2001;    U.S. Pat. No. 6,860,181 issued to P. Aubourg et al., on Mar. 1, 2005.
The first-mentioned document pertains to the assembly of hardware to a window frame. The second document pertains to the joining of frame elements, and the third document pertains to the collating of kits in the manufacturing of aluminium window frames. The collating of the frame elements is done after the cutting and machining of the frame elements.
It is believe that the most important improvements in the manufacturing of vinyl windows can be accomplished during the first part of the process as mentioned before, that is in the frame machining and assembly room. It has been found that most of the idle time and rejects are generated during the cutting of extrusions and the machining and welding of these extrusions into rectangular frames. After analysis of a typical window manufacturing plant, it has been found that the predominant areas of improvement in the plant were:    a) Idle time when searching for material;    b) Defects occurring during welding;    c) Dependence on employee absenteeism.
Idle Time: In a typical window manufacturing plant, a single worker can walk over a distance of 5,200 feet during the production of a single window box. These displacements include primarily the searching of frame elements and the transport of frame elements from inventory to and between work stations. As a consequence, a limited production of 10-12 window boxes per employee per 8-hr-shift has been considered in the past as an acceptable daily production.
Defects Generated During Welding: Although walking time in a manufacturing plant contributes greatly to overall waste, the welding of vinyl extrusions is known to generate numerous defects. Twin head welding machines for example, have different heat characteristics and different melt factors on different extrusion sizes. Both heads in a welding machine may also have different heat characteristics and different melt factors.
When a window frame is welded without taking the melt factors in consideration, the joints on that window frame may not be perfectly square. The amount of material that is melted in a joint is not consistent from one size of extrusion to the next, or from one side of the window frame to the other. As a consequence, the window frame does not have square joints. The opening panel will not fit in that frame, the thermos pane will not fit, and the bug screen will not fit. The brick molding will not fit around that frame either. Therefore, a window frame that is not symmetrical and square must be rejected as waste.
Twin head welding machines are the most popular equipment in the vinyl window frame manufacturing industry and therefore, manufacturers continue to have considerable amount of rejects due to improper welding.
Employee Absenteeism: Employee absenteeism is always a problem for manufacturers, and especially when several work stations depend on each other for a constant supply of workpieces through the plant. During the assembly of window frames for example, the machining of hardware-mounting slots and drain holes must be done before the frame elements are welded together, and the machining cannot start before these frame elements are cut to length. Therefore, the machining center is dependent on the output of the cut-off saw, and the welding machines are dependent on the flow of workpieces through machining center.
In view of these main areas of study, it is believed that there is a need for improvement in the cutting, machining and welding of vinyl window frames. There is still a need in this industry to reduce rejects and to improve productivity and quality.